1. Field of Invention
The present invention relates to an apparatus for digital-to-analog conversion and the method thereof. More particularly, the present invention relates to an apparatus for digital-to-analog conversion comprising a grayscale dithering and the method thereof.
2. Description of Related Art
A conventional grayscale display technique of a thin film transistor liquid crystal display (referred as TFT LCD for short) is to use a timing controller to make a 6-bit source driver circuit generate an approximately 8-bit grayscale effect in a grayscale dithering manner. The grayscale dithering may be classified as a time averaging and a space averaging. Because human eyes have an effect of calculating averages automatically, the displayed screen may be seen to have finer and smoother scale-tuned levels, as long as signals are output in different time scales or space scales.
FIG. 1 is a scale-tuned circuit diagram of a conventional 6-bit source driver circuit, wherein 64 scale-tuned voltages (V0˜V252) may be generated by using divider resistances (R0˜R62) to divide the voltages. FIG. 2 is a circuit diagram of a digital-to-analog converter of the conventional 6-bit source driver circuit, wherein the on and off of switches is controlled by control signals (D0˜D5) respectively, thereby forming 64 conducting paths controlled by the control signals (D0˜D5). Each conducting path is electrically connected to 64 scale-tuned voltages (V0˜V252), which are the same as the scale-tuned voltages (V0˜V252) of the circuit shown in FIG. 1. Through the control signals (D0˜D5), the corresponding scale-tuned voltages (V0˜V252) may be output as an output signal “output” via an output buffer 210.
The output signal “output” may provide any of the 64 different scale-tuned voltages as required. The digital-to-analog converter in FIG. 2 is combined with a timing controller (referred as T-con for short) having a grayscale dithering function. For a single color, the original 64 tuned scales may be raised to 253 tuned scales, but it still cannot achieve the complete 8-bit tuned scales, i.e. 256 tuned scales. The three primary colors displayed with 253 tuned scales may be combined to a color level of 253*253*253≈16.2M, but it still cannot achieve a color effect displayed directly by the 8-bit tuned scales 256*256*256≈16.7M. If the shortage of grayscale tuned scales is to be overcome directly by an 8-bit source driver, the complexity and cost of the circuit will be raised significantly.